Research on Bi contents addition into Sn–Cu-based lead-free solder alloy

This work aimed to investigate the effects of some Bi additions (x = 0, 1, 3, and 5 wt%) added to Sn–2Cu solder alloy on its thermal properties, mechanical performance, and resistance to corrosion, which was investigated by using the Differential scanning calorimetry, Scanning electron microscope, Vickers Hardness Tester, Universal testing machine, Electrochemical workstation, and X-ray diffraction. The experimental results showed that doping 5 wt% Bi could reduce the melting point from 239.7 to 226.6 °C and the undercooling from 24.0 to 9.0 °C, which could improve the thermal properties. Moreover, the Bi addition could refine the microstructure and decrease the CuSn IMC phases’ size. With the addition of 5 wt% Bi, the microhardness and tensile strength reached the highest value of 20.13 HV and 57.64 MPa, respectively, due to the solid solution strengthening and precipitation strengthening. The electrochemical corrosion behaviors were performed to use the potentiodynamic polarization and electrochemical impedance spectroscopy. The obtained results revealed that a dense passivation film was formed on the surface of Sn–2Cu–1Bi alloy to prevent the alloy from being further corroded, which had the lowest value of corrosion current density (0.034 μA·cm) and biggest value of total resistance (200.4 kΩ·cm). Therefore, the Sn–2Cu–1Bi alloy had best corrosion resistance.